Objective: Aim of our study was to evaluate the effectiveness and safety of the preoperative placement of JJ stent compared to not doing in patients undergoing ureteroscopy for ureteral and kidney stone., Materials and Methods: Prospective, observational, multicenter study. Adult patients, who underwent ureteroscopy treatment for ureteral and kidney stone, were recruited from August 2017 to March 2019, in 23 Argentine institutions. The variables analyzed included: demographic data, stone size and location, stone-free rate (SFR) and complications., Results: 580 patients were included. 473 with ureteral stone (309 with and 164 without prior JJ stent) and 107 with kidney stone (77 with and 30 without prior JJ stent). The SFR was higher in the group with previous JJ stent, both in the treatment of ureteral stone (82.2% vs. 90.9%, OR 2.15 (1.17 to 3.96)), and in the treatment of kidney stone (73.3% vs. 89.6%, OR 3.14 (1.02 to 9.61)). No differences were established in the complication rate both in the treatment of ureteral stone (6.1 vs. 6.1%, OR 0.98 (0.45 to 2.19)) and in the treatment of kidney stone (6.7 vs. 5.2%, OR 0.76 (0.13 a 4.46))., Conclusions: The preoperative placement of JJ stent, increases SFR in the treatment of ureteral and kidney stone, but not decrease the complication rate.